[Debugger] Add a ReturnValueScope to correctly handle return values in nested debug breaks.

src/debug/debug.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/debug/debug.h"
 
 #include <memory>
 
 #include "src/api.h"
 #include "src/arguments.h"
@@ skipping 463 matching lines @@
 
   // Return debugger is not loaded.
   if (!is_loaded()) return;
 
   // Clear debugger context global handle.
   GlobalHandles::Destroy(Handle<Object>::cast(debug_context_).location());
   debug_context_ = Handle<Context>();
 }
 
 void Debug::Break(JavaScriptFrame* frame) {
-  HandleScope scope(isolate_);
-
   // Initialize LiveEdit.
   LiveEdit::InitializeThreadLocal(this);
 
   // Just continue if breaks are disabled or debugger cannot be loaded.
   if (break_disabled()) return;
 
   // Enter the debugger.
   DebugScope debug_scope(this);
   if (debug_scope.failed()) return;
 
@@ skipping 1703 matching lines @@
       save_(debug_->isolate_),
       no_termination_exceptons_(debug_->isolate_,
                                 StackGuard::TERMINATE_EXECUTION) {
   // Link recursive debugger entry.
   base::NoBarrier_Store(&debug_->thread_local_.current_debug_scope_,
                         reinterpret_cast<base::AtomicWord>(this));
 
   // Store the previous break id, frame id and return value.
   break_id_ = debug_->break_id();
   break_frame_id_ = debug_->break_frame_id();
-  return_value_ = handle(debug_->return_value(), isolate());
 
   // Create the new break info. If there is no proper frames there is no break
   // frame id.
   StackTraceFrameIterator it(isolate());
   bool has_frames = !it.done();
   debug_->thread_local_.break_frame_id_ =
       has_frames ? it.frame()->id() : StackFrame::NO_ID;
   debug_->SetNextBreakId();
 
   debug_->UpdateState();
   // Make sure that debugger is loaded and enter the debugger context.
   // The previous context is kept in save_.
   failed_ = !debug_->is_loaded();
   if (!failed_) isolate()->set_context(*debug->debug_context());
 }
 
 
 DebugScope::~DebugScope() {
   // Leaving this debugger entry.
   base::NoBarrier_Store(&debug_->thread_local_.current_debug_scope_,
                         reinterpret_cast<base::AtomicWord>(prev_));
 
   // Restore to the previous break state.
   debug_->thread_local_.break_frame_id_ = break_frame_id_;
   debug_->thread_local_.break_id_ = break_id_;
-  debug_->thread_local_.return_value_ = *return_value_;
 
   debug_->UpdateState();
 }
 
+ReturnValueScope::ReturnValueScope(Debug* debug) : debug_(debug) {
+  return_value_ = debug_->return_value_handle();
+}
+
+ReturnValueScope::~ReturnValueScope() {
+  debug_->set_return_value(*return_value_);
+}
+
 bool Debug::PerformSideEffectCheck(Handle<JSFunction> function) {
   DCHECK(isolate_->needs_side_effect_check());
   DisallowJavascriptExecution no_js(isolate_);
   if (!Compiler::Compile(function, Compiler::KEEP_EXCEPTION)) return false;
   Deoptimizer::DeoptimizeFunction(*function);
   if (!function->shared()->HasNoSideEffect()) {
     if (FLAG_trace_side_effect_free_debug_evaluate) {
       PrintF("[debug-evaluate] Function %s failed side effect check.\n",
              function->shared()->DebugName()->ToCString().get());
     }
@@ skipping 163 matching lines @@
     isolate_->Throw(*isolate_->factory()->NewEvalError(
         MessageTemplate::kNoSideEffectDebugEvaluate));
   }
   isolate_->set_needs_side_effect_check(old_needs_side_effect_check_);
   isolate_->debug()->UpdateHookOnFunctionCall();
   isolate_->debug()->side_effect_check_failed_ = false;
 }
 
 }  // namespace internal
 }  // namespace v8